part_of part of part of contained in develops from existence overlaps existence starts during or after material entity Stage 2 Stage 3 Stage 4 Stage 5 primitive ectoderm aboral hemisphere oral hemisphere ciliated epithelial cell primitive ectoderm cell OCLC:82522822 OCLC:464776945 OCLC:20423827 PMID:28072387 Primitive ectoderm cells differentiate from the blastomere population, exit the cell cycle and interact to boud the embryo during Stage 2. Planarian_Anatomy https://orcid.org/0000-0003-2569-1939 | https://orcid.org/0000-0002-7535-4407 https://github.com/obophenotype/planaria-ontology/blob/master/metadata/planarefs/planaref-0000001.md blastomere extraembryonic cell